Method for hydrogenating aromatic polymers in the presence of hydrocarbons which contain oxygen

ABSTRACT

A catayltic process for the hydrogenation of aromatic polymers is disclosed. The catalyst used in the process is a metal or mixture of metals of sub-group VIII of the periodic table together with a support of silicon dioxide, aluminum oxide or a mixture thereof. The catalyst, having pores is characaterized in that the pores having diameters of 100 to 1,000 Å constitute less than 15 percent of the total volume of pores. The hydrogenation, that is carried out in the presence of at least one oxygen-containing hydrocarbon is characterized in that it is essentially complete and without significant degradation of molecular weights.

The invention relates to a process for the hydrogenation of aromaticpolymers, which is characterized in that metals of sub-group VIII arepresent together with a support of silicon dioxide or aluminium oxide ormixtures thereof. The catalysts have a pore size distribution which ischaracterized in that the pore volume between 100 and 1,000 Å is lessthan 15%. The process is carried out in the presence of anoxygen-containing hydrocarbon which accelerates the reaction, andhydrogenates aromatic polymers completely with respect to their aromaticunits and without significant degradation of the molecular weights.

The hydrogenation of aromatic polymers is already known. DE-AS 1 131 885describes the hydrogenation of polystyrene in the presence of catalystsand solvents. Aliphatic and cycloaliphatic hydrocarbons, ethers,alcohols and aromatic hydrocarbons are mentioned as solvents. A mixtureof cyclohexane and tetrahydrofuran is mentioned as preferred. Silicondioxide and aluminium oxide supports of the catalysts are mentionedgenerally, but their physico-chemical structure is not described.

EP-A-322 731 describes the preparation of chiefly syndiotactic polymersbased on vinylcyclohexane, a styrene-based polymer being hydrogenated inthe presence of hydrogenation catalysts and solvents. Cycloaliphatic andaromatic hydrocarbons, but not ethers, are mentioned as solvents.

The ruthenium or palladium catalysts described in DE-OS 196 24835 (=EP-A814 098) for the hydrogenation of polymers, in which the active metal isapplied to a porous support, catalyse the hydrogenation of olefinicdouble bonds of polymers.

It is furthermore known (WO 96/34896=U.S. Pat. No. 5,612,422) that smallpore diameters (200-500 Å) and large surface areas (100-500 m²/g) ofcatalysts assisted by silicon dioxide lead to incomplete hydrogenationand to degradation of the polymer chain in the hydrogenation of aromaticpolymers. The use of specific hydrogenation catalysts assisted bysilicon dioxide (WO 96/34896) allows an almost complete hydrogenationwith approx. 20% degradation of the molecular weights. The catalystsmentioned have a specific pore size distribution of the silicon dioxide,which is characterized in that 98% of the pore volume has a porediameter greater than 600 Å. The catalysts mentioned have surface areasof between 14 and 17 m²/g and an average pore diameter of 3,800-3,900 Å.Dilute polystyrene solutions in cyclohexane (polymer concentrationbetween 1% and a maximum of 8%) are hydrogenated to degrees ofhydrogenation of greater than 98% and less than 100%.

The examples described in the publications mentioned show a degradationof the absolute molecular weights of the hydrogenated polystyrene atpolymer concentrations of less than 2%. Generally, molecular weightdegradation leads to a deterioration of the mechanical properties of ahydrogenated polystyrene.

The comparison example according to WO 96/34896 of a commerciallyavailable catalyst of 5% Rh/Al₂O₃ (Engelhard Corp., Beachwood, Ohio,USA) leads to a degree of hydrogenation of 7% and shows a lower activityof the aluminium oxide support compared with the catalyst assisted bysilicon dioxide.

Surprisingly, it has now been found that if commercially availablestandard hydrogenation catalysts for low molecular weight compoundswhich comprise metals of sub-group VIII, together with a support ofsilicon dioxide, aluminium oxide or a mixture thereof, and which aredefined in that the pore volume between 100 and 1,000 Å is less than 15%are used in the presence of an oxygen-containing hydrocarbon, aromaticpolymers hydrogenate completely and without a significant degradation ofthe molecular weights.

The process is distinguished by the fact that no noticeable degradationof the end product occurs, in particular also at high polymerconcentrations (e.g. >20%). Furthermore, on addition ofoxygen-containing hydrocarbons, an increase in the activity of thecatalyst is to be observed, which manifests itself by lower reactiontemperatures at shorter reaction times for complete hydrogenation(example 2, 3). The addition of this oxygen-containing hydrocarbonallows higher polymer-catalyst ratios for complete hydrogenation thanthe use of purely aliphatic systems. The reactions can be carried outunder identical conditions at lower pressures for completehydrogenation.

The invention provides a process for the hydrogenation of aromaticpolymers in the presence of catalysts and in the presence of anoxygen-containing hydrocarbon, wherein the catalyst is a metal ormixture of metals of sub-group VIII of the periodic table together witha support of silicon dioxide, aluminium oxide or a mixture thereof andthe pore volume of the pore diameter of the catalyst between 100 and1,000 Å, measured by mercury porosimetry, is less than 15% (preferably 2to 12%), based on the total pore volume, measured by mercuryporosimetry. The average pore diameter, determined by mercuryporosimetry, is not more than 900 Å.

However, the mercury method is only sufficiently accurate for poreswhich are greater than 60 Å. Pore diameters of less than 600 Å aretherefore determined by nitrogen absorption, the process according toBarrett, Joyner and Halenda, according to DIN 66 134.

The catalysts additionally have a pore volume, measured by nitrogenabsorption, of 100 to 10%, preferably 80 to 10%, in particular 70 to 15%for pore diameters of <600 Å. The pore volume, measured by nitrogenabsorption, is based on the total pore volume, measured by mercuryporosimetry.

The average pore diameter and the pore size distribution are determinedby mercury porosimetry in accordance with DIN 66133.

The catalysts comprise metals of sub-group VIII, which are presenttogether with a support of silicon dioxide or aluminium oxide ormixtures thereof.

The catalysts characterized in this way have a pore size distributionwhich is characterized in that 100 to 10% preferably 80 to 10%,especially preferably 70 to 15% of the pore volume has a pore diameterof less than 600 Å determined by nitrogen absorption, from the totalpore volume measured by mercury porosimetry (pore diameter of 36.8 Å to13 μm).

The average pore diameter is in general 10 to 1,000 Å, preferably 50 to950 Å, especially preferably 60 to 900 Å.

The specific nitrogen surface areas (BET) are in general 80 to 800 m²/g,preferably 100 to 600 m²/g.

Metals of sub-group VIII, preferably nickel, platinum, ruthenium,rhodium and palladium, are in general used.

The metal content is in general 0.01 to 80%, preferably 0.05 to 70%,based on the total weight of the catalyst.

The 50% value of the cumulative distribution of the particle size in theprocess carried out discontinuously is in general 0.1 μm to 200 μm,preferably 1 μm to 100 μm, especially preferably 3 μm to 80 μm.

The conventional solvents for hydrogenation reactions are used assolvents. These are in general aliphatic and cycloaliphatichydrocarbons, ethers, alcohols and aromatic hydrocarbons. Cyclohexane,tetrahydrofuran or a mixture thereof are preferred.

Some or all the solvent is replaced by an oxygen-containing hydrocarbonor a mixture of such compounds.

Oxygen-containing hydrocarbons are preferably ethers having up to 20carbon atoms and up to 10, preferably up to 6 oxygen atoms, polyetherwith C₁-C₄-alkyl units between the oxygen atoms and molecular weights ofbetween 100 and 100,000 g mole⁻¹, C₁-C₂₀-alkanols orC₁-C₈-alkoxy-C₁-C₈-alkyl compounds, or cyclic ethers having 3-12 carbonatoms and 1 to 6 oxygen atoms.

The alkyl radicals are in each case straight-chain or branched.

Diethyl ether, ethylene glycol diethyl ether, ethylene glycol dimethylether, diethylene glycol dimethyl ether, diethylene glycol diethylether, tetrahydrofuran, dioxane, trioxane and crown ethers, e.g.[18]-crown-6 and [12]-crown-4, are particularly preferred.

The reaction is in general carried out at concentrations of theoxygen-containing component with respect to the total solvent of 0.1% to100%, preferably 1% to 60%, especially preferably 5% to 50%.

The process according to the invention in general leads to a practicallycomplete hydrogenation of the aromatic units. As a rule, the degree ofhydrogenation is ≧80%, preferably ≧90%, especially preferably ≧99% to100%. The degree of hydrogenation can be determined, for example, by NMRor WV spectroscopy.

The starting substances employed are aromatic polymers, which arechosen, for example, from polystyrene which is optionally substituted inthe phenyl ring or on the vinyl group, or copolymers thereof withmonomers chosen from the group consisting of olefins, (meth)acrylates ormixtures thereof. Further suitable polymers are aromatic polyethers, inparticular polyphenylene oxide, aromatic polycarbonates, aromaticpolyesters, aromatic polyamides, polyphenylenes, polyxylylenes,polyphenylene-vinylenes, polyphenylene-ethylenes, polyphenylenesulfides, polyaryl ether ketones, aromatic polysulfones, aromaticpolyether sulfones, aromatic polyimides and mixtures and copolymersthereof, optionally copolymers with aliphatic compounds.

Possible substituents in the phenyl ring are C₁-C₄-alkyl, such as methyland ethyl, C₁-C₄-alkoxy, such as methoxy and ethoxy, or fused-onaromatics which are bonded to the phenyl ring via a carbon atom or twocarbon atoms, such as phenyl, biphenyl and naphthyl.

Possible substituents on the vinyl group are C₁-C₄-alkyl, such asmethyl, ethyl or n-or iso-propyl, in particular methyl in theα-position.

Possible olefinic comonomers are ethylene, propylene, isoprene,isobutylene, butadiene, cyclohexadiene, cyclohexene, cyclopentadiene,optionally substituted norbomenes, optionally substituteddicyclopentadienes, optionally substituted tetracyclododecenes,optionally substituted dihydrocyclopentadienes,

C₁-C₈-, preferably C₁-C₄-alkyl esters of (meth)acrylic acid, preferablythe methyl and ethyl esters,

C₁-C₈-, preferably C₁-C₄-alkyl ethers of vinyl alcohol, preferably themethyl and ethyl ether,

C₁-C₈-, preferably C₁-C₄-alkyl esters of vinyl alcohol, preferably vinylacetate, and derivatives of maleic acid, preferably maleic anhydride,and derivatives of acrylonitrile, preferably acrylonitrile andmethacrylonitrile.

Preferred polymers are polystyrene, polymethylstyrene and copolymers ofstyrene and at least one further monomer chosen from the groupconsisting of α-methylstyrene, butadiene, isoprene, acrylonitrile,methyl acrylate, methyl methacrylate, maleic anhydride and olefins, suchas, for example, ethylene and propylene. Copolymers of acrylonitrile,butadiene and styrene, copolymers of acrylic esters, styrene andacrylonitrile, copolymers of styrene and α-methylstyrene and copolymersof propylene, diene and styrene, for example, are possible.

The aromatic polymers in general have molecular weights (weight-average){overscore (M)}_(w) of 1,000 to 10,000,000 preferably 60,000 to1,000,000, particularly preferably 70,000 to 600,000, in particular100,000 to 480,000, determined by light scattering.

The polymers can have a linear chain structure and can also havebranching positions due to co-units (e.g. graft copolymers). Thebranching centres comprise e.g. star-shaped polymers or other geometricshapes of the primary, secondary, tertiary or optionally quaternarypolymer structure.

The copolymers can be present both randomly, in alternation and asblocked copolymers.

Block copolymers comprise di-blocks, tri-blocks, multi-blocks andstar-shaped block copolymers.

The amount of catalyst to be employed is described, for example, in WO96/34896.

The amount of catalyst to be employed depends on the process to becarried out; this can be carried out continuously, semi-continuously ordiscontinuously.

In the continuous system, the reaction time is considerably shorter; itis influenced by the dimensions of the reaction vessel. In thecontinuous procedure, the trickle system and the sump system, both withcatalysts arranged in a fixed bed, are just as possible as a system withcatalyst which is suspended and e.g. circulated. The catalysts arrangedin a fixed bed can be present in tablet form or as extrudates.

The polymer concentrations, based on the total weight of solvent andpolymer, in the discontinuous process are in general 80 to 1, preferably50 to 10, in particular 40 to 15% by weight.

Methods for characterizing hydrogenation catalysts are described e.g. inWO 96/34896 (=U.S. Pat. No. 5,612,422) and Applied HeterogenousCatalysis, Institute Francais du Petrole Publication, page 189-237(1987).

The reaction is in general carried out at temperatures between 0 and500° C., preferably between 20 and 250° C., in particular between 60 and200° C.

The reaction is in general carried out under pressures of 1 bar to 1,000bar, preferably 20 to 300 bar, in particular 40 to 200 bar.

EXAMPLES

The absolute molecular weights {overscore (M)}_(w) (weight-average) ofthe starting polymer and of the hydrogenated product are determined bylight scattering. Membrane osmosis gives the absolute molecular weight{overscore (M)}_(n)(number-average). In examples 3, 4 and 5, therelative values of the GPC measurement with respect to polystyrenestandards correspond to the absolute molecular weights determined forthe polystyrene employed.

Examples 1-5

A 11 autoclave is flushed with inert gas. The polymer solution and thecatalyst are added (table 1). After closing, the autoclave is chargedseveral times with inert gas and then with hydrogen. After letting down,the particular hydrogen pressure is established and the batch is heatedto the corresponding reaction temperature, while stirring. The reactionpressure is kept constant after the uptake of hydrogen has started.

The reaction time is the time from heating up the batch to completehydrogenation of the polystyrene or, in the case of incompletehydrogenation, the time up to which the uptake of hydrogen tends towardsits saturation value.

When the reaction has ended, the polymer solution is filtered. Theproduct is precipitated in methanol and dried. The product isolated hasthe physical properties shown in table 1.

The catalysts employed are characterized in table 2.

TABLE 1 Hydrogenation of polystyrene as a function of the catalyst,solvent system and reaction temperature Reaction H₂ Degree of Tg{overscore (M)}_(n) {overscore (M)}_(w) Catalyst Polymer Catalysttemperature pressure Reaction hydrogenation¹⁾ (DSC) 10³ 10³ Example no.no. weight g Solvent³⁾ ml weight g ° C. bar time h % ° C. g/mole g/moleComparison 1 1 100.2²⁾ 300 CYH 12.5 160 100 13  98.5 148 70.0 170.4Comparison 2 1 100.2²⁾ 300 CYH 12.5 200 100 7 100 148 47.5 108.1 3according to 1 100.2²⁾ 200 CYH + 12.5 160 100 7 100 148 69.8 176.4 theinvention 100 THF 4 according to 2 100.2²⁾ 200 CYH + 12.5 160 100 7 100148 70.1 178.2 the invention 100 THF 5 according to 2 100.2²⁾ 200 CYH +12.5 160 100 7 100 148 69.7 177.3 the invention 100 Glyme ¹⁾Determinedby ¹H-NMR spectroscopy ²⁾Polystyrene type 158 k, {overscore (M)}_(w) =280,000 g/mole, BASF AG, Ludwigshafen, Germany ³⁾CYH = cyclohexane THF =tetrahydrofuran Glyme = ethylene glycol dimethyl ether

TABLE 2 Physical characterization of the catalysts employed Pore volumeNitrogen pore Total mercury (measured by mercury Pore volume for volumefor pore volume for N₂ pore volume for porosimetry) for pore diameterspore diameter pore diameter pore diameters <600 pore diameters 100-1000Å total Average Specific total Catalyst no.$\frac{< {600\quad Å}}{{mm}^{3}/g}$

$\frac{{36.8\quad Å} - {13\quad {\mu m}}}{{mm}^{3}/g}$

Å/total mercury pore volume %$\frac{100\quad {Å–1000}\quad Å}{{mm}^{3}/g}$

pore volume (measured by mercury porosimetry) % pore diameter¹ Å surfacearea (BET)² m²/g Metal content % 1 275 1,088 25 110 10 333 142 62.2 2280 1,l58 24 130 11 412 132 62.8 Catalyst no. 1: Aldrich, Steinheim,Germany, nickel on silicon dioxide/aluminium oxide, order no. 20 877-9Catalyst no. 2: Engelhard, De Meern B.V., The Netherlands Ni-5136P,nickel on silicon dioxide/aluminium oxide ¹Average pore diameter bymercury porosimetry (DIN 66 133) ²Specific nitrogen total surface areain accordance with Brunauer, Emmett and Teller (BET, DIN 66131, DIN66132)

The nickel catalyst (table 1) hydrogenates polystyrene at 160° C. in areaction time of 13 hours incompletely to the extent of 98.5%(comparison example 1). At 200° C., complete hydrogenation is alreadyachieved after 7 h, but with a drastic decrease in the molecular weight(comparison example 2). On the other hand, the process according to theinvention leads to a reduction in the reaction temperature required forcomplete hydrogenation with a far shorter reaction time and whileretaining the absolute molecular weights {overscore (M)}_(n) and{overscore (M)}_(w), compared with the starting polymer (example 3, 4,5).

What is claimed is:
 1. A process comprising, hydrogenating an aromaticpolymer in, (a) a solvent comprising, (i) a hydrocarbon selected from atleast one of a cycloaliphatic hydrocarbon and an aliphatic hydrocarbon,and (ii) at least one oxygen-containing hydrocarbon,  in the presence of(b) a catalyst comprising, (i) a support comprising at least one ofsilicon dioxide and aluminum oxide, and (ii) at least one metal ofsub-group VIII of the periodic table of the elements, wherein saidcatalyst has pores having a pore diameter of 100 to 1000 Å whichconstitute less than 15 percent of the total volume of pores, said porevolume being determined by mercury porosimetry, and 80 to 10% of thepore volume constitute pores having diameters smaller than 600 Å.
 2. Theprocess of claim 1 wherein said hydrocarbon (a)(i) is cyclohexane, andsaid oxygen-containing hydrocarbon (a)(ii) is selected from at least oneof tetrahydrofuran and ethyleneglycol dimethyl ether.
 3. The process ofclaim 1 wherein said metal (b)(ii) is selected from nickel.
 4. Theprocess of claim 1 wherein 70 to 15% of the pore volume constitute poreshaving diameters smaller than 600 Å.
 5. The process of claim 1 whereinsaid oxygen-containing hydrocarbon (a)(ii) is at least one memberselected from the group consisting of ethers having up to 20 C atoms andup to 6 oxygen atoms, polyethers with C₁-C₄-alkyl units between theoxygen atoms and molecular weights of 100 to 100,000 g/mole, C_(1-C)₂₀-alkanols, C₁-C₈-alkoxy-C₁-C₈-alkyl compounds and cyclic ethers having3 to 12 C atoms and 1 to 5 oxygen atoms.
 6. The process of claim 1wherein said oxygen-containing hydrocarbon (a)(ii) is at least onemember selected from the group consisting of diethyl ether, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycoldimethyl ether, diethylene glycol diethyl ether, tetrahydrofuran,dioxane, trioxane and crown ethers.
 7. The process of claim 1 whereinsaid oxygen-containing containing hydrocarbon (a)(ii) is present in aconcentration of 1 to 60%.